Floating vs Lab Thermometer

When I am mashing, why does this thermometer (floating)

http://www.northernbrewer.com/pics/fullsize/floating thermometer.jpg

Read different than this one? (Lab)

http://www.northernbrewer.com/pics/fullsize/lab-thermometer.jpg

And which one do I trust.

The floating one is placed in the mas vertically. Should It be in there horizontally for an accurate reading. The floating one says I am right on for my mash temp, the lab one says I am about 6* lower...

Just put them both in Boiling water to check calibration and they both read 212 on the Dot (line...lol) The floating one just took a little longer to get there. My gut tells me to trust the floating one...

I had a floating thermometer that said my water boiled at 205. Scared the crap out of me because I noticed mid mash that my floater said I was at 143 when I was aiming for 150 in my mash. I couldn't figure out how I missed so badly. Threw that thing away.

Linc

Hmmm interesting.

Mine seems to be the reverse problem

Floating one says temp is higher not lower than the lab thermo.

This is exactly why it's so important to calibrate your thermometer. I check mine periodically, whenever I get boiling water going, for whatever reason.

Just be careful if your at elevation, water boils at lower temps than 212f.

My floater reads lower than my lab by about 6*.

Make sure your lab thermometer is immersed properly.

Mine has a white line for minimum immersion depth at about 8" on a 14" thermometer.

You wouldn;t think it matters much. But it does.

GilaMinumBeer said:

Make sure your lab thermometer is immersed properly.

Mine has a white line for minimum immersion depth at about 8" on a 14" thermometer.

You wouldn;t think it matters much. But it does.

Click to expand...

Seriously, mine is a Total Immersion which means the whole thing has to be in the liquid to get a really accurate reading. I usually leave it about an inch below the reading.

Im having all kinds of issues with my thermometers also my floater reads 200 at boiling.

Gila, glad you mentioned that. I just looked on my lab thermometer and it says "total immersion". Looks like I need to calibrate again.

I have 3 or 4 floating thermometers and they ALL read different temperatures....needless to say I do not trust them and no longer use them.

I have a digital probe thermometer that works great. I always check the calibration on it prior to any brew.

As far as checking calibration I would not use boiling water. Water boils at various temperatures at different levels. For example here in Denver the average boiling point is around 200F, compared to sea level where it is 212F. So instead pack a glass full of ice and fill it with water, allow it to rest for a bit then insert your thermometer. Although not frozen it should read 32F. This will work correct regardless of your elevation.

This is another reason I love my Thermapen. I also bought another waterproof silicone probe and meter from them and just leave the thing in the mash tun to monitor temps with the MLT closed the whole time. Then I clean and sanitize it, so that when I transfer to the fermenter I can accurately monitor my actual fermentation temps as well.

I've given up on analog thermos, I can never get one that reads quite right. I've switched to a digital with changable probes so I can leave long wire probes in my HLT and my mash tun threaded through the lid to get reading when I need to without opening it, and I have an extra straight probe with a handle for reading other things like the temp of the water for rehydrating yeast.

Buford said:

I've given up on analog thermos, I can never get one that reads quite right. I've switched to a digital with changable probes so I can leave long wire probes in my HLT and my mash tun threaded through the lid to get reading when I need to without opening it, and I have an extra straight probe with a handle for reading other things like the temp of the water for rehydrating yeast.

Click to expand...

i'm with Buford, for something thats so important, analogs were doing nothing but pissing me off. I plopped down a few extra dollars on a good digital with different probes and am much more satisfied.

I've got the floater and the one that came free with my 10 Gal aluminum pot, round analog dial on a long metal probe.

Both of them suck in their way, both of them are quite handy in others.

I honestly think the floater is accurate - it's just got such a slow equilibration time that it is nearly useless in the mash. I leave it floating in there, but I kind of get a sick feeling when I stir around in the mash and find pockets where the temperature seems warmer or lower. It's very hard to tell, with that thermometer, whether those spots are real or not and when I've stirred to uniformity. Also hard to tell when I've tweaked to hit my mash temp.

The one with the metal probe responds much more quickly, but has very little precision. I have to guesstimate the temps, because there are so few increments...

The floater has its place, in the water bath that I use to set my fermentation temp. I use the one with the probe to see how close I am to getting my boil, and as a backup for the floater, but not for much else.

You may notice that I don't have one that is good for the mash. That's my next purchase. Preferably a combo thermometer/pH meter.

Another vote for thermapen. People on this board turned me onto it. Expensive, but good. Since I cook a lot as well, it was definitely worth the price. A lot of things in brewing we can DIY or do on the cheap but the thermometer may not be one of them.

commonlaw said:

A lot of things in brewing we can DIY or do on the cheap but the thermometer may not be one of them.

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+1 to that. The thermometer may be your most important brewing accessory for all grain. You have to get those mash types right when 2 degrees makes such a big difference.

I know this is the expensive route, but seriously, thermapen.

A point brought up by my brew club (Maltose Falcons) was the actual marking your read off a hydrometer is just a piece of paper stuck in a glass tube. If you bang the hydrometer, you can shift the paper, making it worthless (now I have two hydrometers.)

If you take a look at your floating thermometer, most of them work the same way. I suppose it is even possible the paper you read off of might not be entirely straight, and read more or less accurately in some ranges, but not in others. Either way, one good bang (as happened to me) and you could be mashing 10-20 degrees off. Ouch.

cmoon said:

A point brought up by my brew club (Maltose Falcons) was the actual marking your read off a hydrometer is just a piece of paper stuck in a glass tube. If you bang the hydrometer, you can shift the paper, making it worthless (now I have two hydrometers.)

Click to expand...

I do an imprecise calibration of my hydrometer before every brew. I just put it in some water (don't mess with distilled) at approximately 60 degrees and see if its reading 1.000. It may be a point or two off for temperature or impurities in the water, but this is a good basic sanity check.